I plan to build my first SBR sometime in the upcoming months.

What's the optimal barrel length for a 5.56 SBR?

Will most use as a range toy, 0-200 yards most likely. May use as home defense with my pistol.

Would like to eventually put a suppressor on it so keep that in mind.

Many thanks!

10.3 - 11.5" for under 200

I like around 12"

With the right ammo you'll be good to about 275 with legit rifle wounding performance from a 10.5".  Go with an 11.5" for extra margin of reliability and 300yds, many recommend 12" for a bit more velocity still-- kind of a sweet spot compromise length.  For your parameters shorter might be handier though..  Use Federal Fusion MSR 62gr for general purpose/barriers and Black Hills 75gr TMK for over-penetration sensitive situations like home defense.

11.5. More dwell time/operating parameters than 10 or 10.5. And more velocity than you'd think.

I did quite a lot of reading on the subject, 11.5" seems to be the the one with the best advantage/ disadvantage ratio.

What ammo will I be able to use in my SBR?

I have thousands of rounds of M193 ... will this work or will I have to get dedicated ammo for it?

12.5" give the best bang for your buck when you look at the ballistics.  

My 12.5" Noveske with Form 1 Ti reflex can.  

11.5-12.5 seems to be the sweet spot for balancing velocity loss with length.

11.5

I have an 11.5" 6.8 and a 10.5" 5.56 and both are suppressed. It is surprising how much handier the 10.5" is given the pretty minimal length difference (about 1.25" or so due to different suppressor lengths.)

I hunt predators and hog with these rifles, and, especially at night, the difference really shows.

The 62gr Federal Fushion MSR ammo is good stuff and works well on targets as variable as hogs and coyotes, fox, raccoons, opossums. I wouldn't hesitate to use this ammo for HD. I would not choose XM193 for HD in any situation out of any rifle. Repelling leftist hordes... yes...

For practice, training, plinking, anything should work. It is not difficult to set up a 10.5" or 11.5" rifle to function properly.

I'd suggest saving some time and effort and maybe some problems down the road and installing an adjustable gas block so that when you get your suppressor you can tune the gas properly, or even before you get your suppressor depending on gas port size.

JPK

I'm looking at either a 10.5 or 11.5 as well, planning on eventually getting a suppressor. That said, I plan on getting a complete upper because I've never put one together and don't have much of a workspace to do it (and i don't want to fuck it up ). If i get a complete upper, how difficult is it to install an adjustable gas block?

With a typical non-pinned gas block and a typical hand guard it isn't difficult. You would remove the muzzle device, the hand guard and then loosen the gas block and slide it off. Slide the new adjustable gas block on and then reinstall the hand guard and muzzle device. Some blocks are easier to slide off or on, some are more difficult, but none I've messed with were too tough.

You would want to make sure your new, adjustable block is lined up with your barrel's gas port before tightening the clamp on screws or set screws.

Pinned gas blocks are another thing. A royal pita in my limited experience with them. Blind pinned = send it out for me. KAC URX hand guards are also a pita and need timing and a special wrench.

Some builders offer adjustable gas blocks as an option when you order an upper, but surprisingly few. Chances are excellent that your upper would function without an adjustable gas block, but it will have less and smoother felt recoil with gas adjusted properly, less fouling, less heat build up, less gas out the action. Once in awhile bolt speed is too excessive with a suppressor and a non-adjustable gas block and the bolt doesn't pick up rounds off the magazine, or occasionally the bolt won't lock back (which is more often a sign of insufficient gas) but not very often.

JPK

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